Despite the outcry over The Mail on Sunday’s revelations that police were hacking its journalists’ phones, police are still refusing to reveal the scale of the snooping.

At least four forces across Britain – as well as the taxman – have been exposed for using controversial anti-terror powers to expose sources and trace leaks.

But they are still blocking requests from journalists to reveal the full details of their surveillance conducted under the Regulation of Investigatory Powers Act 2000 (RIPA).

Kent Police obtained records of this newspaper’s phone calls in order to trace the confidential source of our stories about shamed Cabinet Minister Chris Huhne, who had falsely accused journalists of conspiring to bring him down over his illegal penalty points swap with his wife. Last night the force – while claiming it ‘welcomed a wider debate’ about RIPA – declined to answer key questions about the controversial investigation.

It would not say how many phone numbers were trawled through as part of the probe – codenamed Operation Solar – into Huhne’s bogus claim that he was the victim of a conspiracy.

Nor would Kent say how many individuals were identified after their private numbers were revealed through the RIPA application to telecoms companies.

And the force would not say what had happened to the data since the probe in 2012 – raising the prospect it is still lying in police files.

The force would also not identify the senior officers who had approved the RIPA application, only saying it was a superintendent and an inspector.

Assistant Chief Constable Matthew Horne said in a statement: ‘We welcome a wider debate on whether this specific investigatory power – when used in lawful pursuit of serious wrongdoing – should be the subject of judicial authority or oversight from an appropriate regulatory body when matters of journalistic privilege are apparent. As part of this debate consideration has to be given to how material held by the media that might be relevant to a criminal investigation is shared with the police and the courts.’

Police forces across the country failed to reveal how many times reporters have been monitored using RIPA.

Share this article

Of the 37 forces who rejected Freedom of Information requests by industry journal Press Gazette, 24 said it would cost too much to trawl through their records, while 13 cited security reasons.

However, every chief constable has now been ordered to provide the information both by a watchdog and MPs.

The Interception of Communications Commissioner, Sir Paul Kennedy, has told all chief constables to hand over ‘full details of all investigations that have used Part I Chapter 2 RIPA powers to acquire communications data to identify journalistic sources’.

And the chairman of the Home Affairs Select Committee, Keith Vaz, said: ‘I will be writing to them, each of the police forces, to ask how many times they’ve used RIPA powers and where. I’d like it broken down by profession.’

Sources said it will be a huge undertaking for police as, until now, they have not been required to collate figures on how many times they have accessed journalists’ data since the law came into force in 2000.

The records cannot be searched in a single database, so police staff will have to painstakingly reopen every single RIPA application made over the past 14 years to see if it makes reference to journalistic sources. Figures obtained by pressure group Big Brother Watch show police made more than 120,000 RIPA requests for communications data in a single year – 2011-12 – so the total number of files to be searched will top one million.

As well as Kent, it is known that three other forces, as well as HMRC tax officers, have used RIPA in leak investigations.

Ian Hislop called the police's actions 'dangerous' and said 'if they can do it to journalists they can do it to all of you'

Scotland Yard trawled through phone data for The Sun’s political editor Tom Newton Dunn so detectives could track down the source of the ‘Plebgate’ story that led to Tory Chief Whip Andrew Mitchell resigning. The Met refused to say how many times it had used RIPA in leak inquiries.

Thames Valley Police bugged the car of local newspaper reporter Sally Murrer in a 19-month leak inquiry that ended with the case against her collapsing.

The force declined to comment on her case but said: ‘RIPA is designed to ensure the powers are used lawfully and in a way that is compatible with human rights. It also requires those authorising the use of covert techniques to give proper consideration to whether their use is necessary and proportionate.’

Suffolk Police obtained phone records of a reporter on the Ipswich Star, Mark Bulstrode, to find out how he had got a story about a rape investigation – even though his paper did not run the controversial piece.

HMRC also used the law to get hold of phone records for one of its own solicitors, Osita Mba, after it wrongly thought he had told a newspaper about a secret deal with millionaire bankers. The taxman declined to say how many times it had used RIPA on its own employees.

Last night, police chiefs insisted they took great care when using RIPA, and promised to co-operate with the watchdog’s inquiry.